A component constituting an automotive silencer, for example, an end plate is manufactured by press forming of a sheet material. The conventional typical method consists of four processes: the outer periphery portion of a sheet material is cut (trimmed) to form a predetermined blank, a predetermined formed surface in the central portion of the blank is drawn, a predetermined non-formed surface in the central portion of the blank is pierced to form a pierced hole (pipe mounting hole), and finally burring around the pierced hole in the blank and bending of the outermost portion of the blank are performed, thereby obtaining an end plate product.
As a press forming method for a sheet material, a press forming method in which the drawing and the secondary working of a sheet material are performed by one cycle of pressing operation has been known (for example, refer to FIG. 1 of Patent Document 1).
In the forming method described in this publication, an upper die to which a punch is installed via an elastic means is lowered with respect to a lower die on which a blank is set, by which a sheet material is drawn by the upper and lower dies. Then, an upper cutting blade mounted on the upper die is projected downward by the lowering of the upper die, whereby the outer periphery portion of the sheet material is trimmed or trimmed and downwardly bent by the upper cutting blade and a lower cutting blade mounted on the lower die. Next, the lower cutting blade is projected upward by the lowering of the upper die, whereby the outer periphery portion of the sheet material is upwardly bent by the upper cutting blade and the lower cutting blade.
With this forming method, three processes of drawing, and outer periphery trimming and outer periphery bending, which are secondary working operations, can be performed by one pressing operation, but further secondary working operations cannot be performed simultaneously by this pressing operation. Therefore, for example, in the case where the above-mentioned silencer end plate is manufactured, piercing and burring must be performed separately, so that the shortening of pressing operation time is limited. Also, an independent die for piercing operation etc. is required. Therefore, the reduction in die cost is not so big.
Also, since the outer periphery trimming operation and the outer periphery bending operation are performed in succession after the drawing operation has been finished, this method has a drawback in that the working stroke is long. Furthermore, since the cutting blades for cutting the outer periphery are not fixed to the upper and lower die set and are movable, there arises a problem in that a backup mechanism (guide mechanism) is needed.    Patent Document 1: Japanese Patent Laid-Open No. H08-290219